I have seen that in other players (including a catcher). The catcher said it hurt on the inside of the elbow right below the bicep area (ached pretty bad). After she went to the doctor she was told she had bicep tendonitis. Doctor recommended rest--especially from throwing down to second base.
She worked on her mechanics, which had not changed since she was younger--or so she thought. She hasn't had anymore trouble since, but she did take a few months OFF from throw downs, and spent time on her mechanics.
MADE A HUGE DIFFERENCE
..sometimes we think the mechanics are fine (or they make subtle changes that aren't noticed), might be worth taking her to someone to evaluate her throwing??
good luck
